The present application is relevant to U.S. patent Ser. No. 10/462,904, and some disposable electrochemical sensor strips with metal electrodes are provided. The electrochemical sensor strips of the present application are suitable for testing the contents of some specific analytes in a sample, especially in a fluid sample. For example, it is possible to test one or more concentrations of glucose, cholesterol, and uric acid in the human blood, or one or more concentrations of the insecticides, pesticides, fungicides, herbicides, heavy metals and so forth in a polluted water by the present invention. In other words, the electrochemical sensor strips according to the present application are suitable to be used in any kind of electrochemical sensors, bio-sensors, fluid biochemical sensors, and some domestic medical sensors (e.g. blood glucose sensor).
In recent decades, the principle of electrochemical sensor has been developed and applied in the field of detecting kinds of fluid ingredients. An electrochemical sensor may be assembled with different equipments due to their different application fields. Nevertheless, an electrochemical sensor in a general laboratory is generally different from that in a professional checking room. A basic framework of an electrochemical sensor includes the following components:
1. A container, which is applied to contain a fluid sample and is a region for measuring an electrochemical reaction;
2. A chemical reagent, which is used for chemically reacting with an analyte contained in the fluid sample and generating an output signal with an electric parameter, wherein the electric parameter is corresponding to an ingredient of the analyte contained in the fluid sample. For example, if the fluid sample is the human blood and the analyte is the glucose, the chemical reagent would be basically a glucose oxidase and a complex thereof;
3. Plural testing electrodes, which are selected from a group consisting of a counter electrode, a working electrode, a reference electrode, and a detecting electrode; and
4. A measuring device, such as an electrochemical meter, which provides the essential working voltage (or current) needed by the electrochemical reaction and measures the electric parameter (output voltage or current) produced by the electrochemical reaction to be recorded for processing the numerical analysis and displaying the testing result thereon.
In general, the plural testing electrodes can include the counter electrode and the working electrode, the reference electrode and the working electrode, or the counter electrode, the working electrode, and the reference electrode. Moreover, a detecting electrode could be included as a fourth electrode, if necessary. The number of the plural testing electrodes is varied according to the requirements of the electrochemical reaction.
The functions of the plural electrodes are mutually different from each other, and the plural electrodes are made of different materials. In the general laboratory, the counter electrode is made of any conductive material, where one of a lower conductive resistance is the better, such as a copper, a silver, a nickel, a graphite, a carbon, a gold, a platinum or other conductive materials, or can be a conductive membrane electrode formed by printing a carbon paste or a silver paste on a conductive material. The most common reference electrode is a modified electrode produced by means of printing or electroplating an Ag/AgCl film. Because the electrochemical electric potential of the Ag/AgCl film is quite stable, it is extensively used as the reference electrode.
The selection of the materials for the working electrodes is more complex and the working electrodes can be categorized as two types according to the used materials. One kind of the working electrode is an electron-transfer mediator modified working electrode, and the other is a metal-catalyzed electrode. The electron-transfer mediator modified working electrode has a chemical reagent immobilized thereon, wherein the chemical reagent includes an enzyme (such as a glucose oxidase) and a redox mediator (such as a potassium ferricyanide, which is extensively used in the glucose testing strip). The enzyme and the analyte will react with each other to produce a new chemical compound (such as H2O2), the electrons generated from the redox reaction between the electron mediator and the new chemical compound (such as H2O2) is utilized to produce an electric signal, and through the electrode, the electric parameter corresponding to the electric signal can be outputted. The main purpose of this kind of working electrode is only simply a conductor and is not involved in any chemical catalysis. However, the material used to make the electrodes should be selected specifically, so as to avoid the chemical reaction occurring between the electrodes and the fluid sample or between the electrodes and the chemical reagent thereby interfering the testing result.
The electrode without the chemical interference should be made of an inert conductive material, which is generally a noble metal (such as a gold, a platinum, a palladium, or a rhodium), or a carbon containing material (such as a carbon base screen printing electrode or a graphite bar). Furthermore, because the carbon and the noble metal have no chemical reactivity in a low temperature, the chemical interference would not happen. However, because the noble metal is a little bit expensive, the carbon made electrode is usually applied as the electron-transfer mediator modified working electrode.
As to the metal-catalyzed electrode, it is made of a material which will directly electrochemically react with the chemical reagent, the analyte, or the derivatives thereof, and have an ability of direct catalysis or a function of a single selectivity for the analyte. Thus, no electron mediator is needed to be added into the chemical reagent. This kind of electrode, not like the electrode only needing to be made of a chemically inactive metal, is generally made of a material that must have an ability to catalyze the reaction. Therefore, the material thereof should not be limited to be a noble metal but matched with the analyte, such as a copper, a titanium, a nickel, a gold, a platinum, a palladium, or a rhodium . . . etc., (in which, a rhodium electrode has an excellent ability to directly catalyze H2O2).
U.S. Pat. No. 5,997,817 had disclosed a metal electrode. In this patent, two conductive metal tracks coated by a palladium are fixed on an insulating substrate for being the metal electrodes (such as a working electrode and a counter electrode). However, the positions that are necessarily formed by palladium are only two tiny sections of the metal electrodes, and the other portions need only be formed by materials having a conductive characteristic rather than being noble metal-palladium. Thus, it would be a waste to coat the palladium onto all the surfaces of the metal electrodes.
In addition, U.S. Pat. No. 5,985,116 had disclosed a disposable printing electrochemical sensor strip. The electrodes on the sensor strip are formed by printing some conductive pastes onto the insulating substrate. However, the sensitivities of the electrodes are determined by the materials of the conductive pastes. If the conductive pastes are made of a noble metal, the sensitivity of the relevant electrodes will be greater, the unnecessary chemical interference would be reduced, but the corresponding cost will be high. On the contrary, in order to decrease the relevant cost, the conductive pastes might be made of a low-cost conductive material, such as the carbon. However, the sensitivity of the relevant electrodes made of a low-cost material will not be so good due to the impedance thereof.
As above, although the use of the electrochemical sensor strips has become the main trend of the domestic medical applications (such as the sensor strips for testing the blood glucose, the uric acid, or the cholesterol contents in the human blood), some problems about the testing accuracy and the relevant cost are still awaiting to be overcome.
Please refer to FIG. 1, which is a flow chart showing the manufacturing process of an electrochemical sensor strip in the prior art. As shown in FIG. 1, the manufacturing process includes the following steps: 1. An insulating substrate is provided. 2. Some electrodes are located on the insulating substrate. 3. A reaction concavity is assembled on the insulating substrate. 4. An electrochemical reaction layer is formed in the reaction concavity by applying a chemical reagent therein. 5. The reaction concavity is sealed after the chemical reagent is dry. 6. An opening located on the side edge of the insulating substrate is formed by a step of eroding.
Please refer to FIGS. 2(A)-2(B), which are the schematic diagrams showing the different statuses of the electrochemical sensor strip during the step of eroding in the prior method. In addition, please refer to FIG. 2(C), which is the schematic diagram showing the status of the fluid sample during the testing step in the prior method. As shown in FIGS. 2(A)-2(C), the electrochemical sensor strip 3 includes the insulating substrate 31, the electrodes 32, the electrochemical layer 33, the reaction cavity 34, the cover 35 and the air hole 37. As shown in FIG. 2(A), the reaction concavity 34 is peripherally and entirely enclosed before a step of eroding. As shown in FIG. 2(B), the opening 36 is formed on the side edge of the electrochemical sensor strip 3 after the electrochemical sensor strip is eroded. In addition, there are some cracks 331 that will be formed due to the mechanical force resulting from the step of see eroding. As shown in FIGS. 2(B)-2(C), however, since there are some cracks 331 on the electrochemical layer 33, it is possible that the testing sample A would be contacted with the electrodes 32 before being reacted with the electrochemical layer 33 so that the electrochemical reaction between the testing sample A and the electrochemical layer 33 might be affected by the cracks 331. As the above discussions, it would be found that the step of eroding is the main reason of the undesired testing accuracy of the electrochemical sensor strip 3.
According to the technical defects described above, for reducing the manufacturing cost of the metal electrode in the sensor strip and overcoming the problems of the structural damage, the applicant has devoted himself to develop another electrochemical sensor strip through a series of experiments, tests and researches. In addition to effectively solving the wasting problem of the noble metal and avoiding the relevant damaging manufacturing procedure in the prior arts, the present application further provides more complete structures of the electrochemical reaction layer for increasing the testing accuracy accordingly. Furthermore, the sensor strip according to the present invention can be applied to kinds of electrochemical testing devices, such as biosensor strips, fluid biochemical sensor strips (e.g., the testing strips for a sewage, a pesticide content, a heavy metal ingredient etc.), and kinds of domestically medical application testing strips (e.g., the testing strips for a blood glucose, a uric acid, and a cholesterol).